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Expression of an isoform of the novel signal transduction protein ST5 is linked to cell morphology
A E Hubbs1, M Majidi, J H Lichy
1Department of Cellular Pathology, Armed Forces Institute of Pathology, Washington, DC 20306-6000, USA.
Abstract:
The human ST5 gene is expressed as 4.6, 3.1 and 2.8 kb transcripts encoding putative 126, 82 and 70 kDa proteins that function in the MAP kinase signaling pathway in transient expression assays. Expression of the 2.8 kb transcript correlates with reduced tumorigenicity in HeLa-fibroblast hybrids, suggesting a role in tumor suppression. We now report the detection of ST5 proteins in cellular extracts, demonstrate specific expression of p70 in non-tumorigenic HeLa-fibroblast hybrids, extend the correlation between p70 expression and cellular morphology to a wide variety of cell lines, and provide direct evidence that p70 can effect changes in cell growth and morphology. ST5 proteins were identified in extracts of human, mouse and simian epithelial cells and fibroblasts, but were absent from lymphoid cells. Transfection of the 2.8 kb cDNA into a p70-negative mouse fibroblast line yielded stable transfectants with a flattened, less refractile morphology relative to controls. The p70 expressing clones had initial growth rates similar to those of control cells but their saturation density was reduced threefold, suggesting a restoration of contact-regulated growth. In conjunction with previous findings, these results suggest that ST5 proteins participate directly in events affecting cytoskeletal organization and tumorigenicity.
Insights
The ST5 gene
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- The human ST5 gene expresses multiple transcripts, producing proteins involved in the MAP kinase signaling pathway.
- Expression of the 2.8 kb ST5 transcript correlates with reduced tumorigenicity in hybrid cells, suggesting a tumor suppressor role.
Purpose of the Study:
- To detect ST5 proteins in cellular extracts.
- To demonstrate specific expression of the p70 protein in non-tumorigenic cells.
- To investigate the role of p70 in cell growth, morphology, and tumorigenicity.
Main Methods:
- Detection of ST5 proteins in human, mouse, and simian cell extracts.
- Analysis of ST5 protein expression in various cell lines, including HeLa-fibroblast hybrids.
- Transfection of ST5 cDNA into p70-negative mouse fibroblasts to assess effects on cell morphology and growth.
Main Results:
- ST5 proteins were detected in epithelial cells and fibroblasts but absent in lymphoid cells.
- Specific expression of p70 was observed in non-tumorigenic HeLa-fibroblast hybrids.
- Transfected cells exhibited altered morphology and reduced saturation density, indicating restored contact-regulated growth.
Conclusions:
- ST5 proteins, particularly p70, are expressed in specific cell types and correlate with non-tumorigenic phenotypes.
- p70 expression influences cytoskeletal organization, cell morphology, and contact-regulated growth.
- These findings suggest ST5 proteins play a direct role in tumor suppression and cytoskeletal regulation.